Kautilya's Arthashastra 2.13.22

2.13.22

samarāgī vikrayakrayahitaḥ //

A touch-stone with soft and shining splendour is the best. The touch-stone of the Kálinga country with the colour of green beans is also the best. A touch-stone of even or uniform colour is good in sale or purchase (of gold). That which possesses the colour of an elephant, tinged with green colour and capable of reflecting light (pratirági) is good in selling gold. That which is hard, durable, and of uneven colour and not reflecting light, is good for purchasers (krayahitah). That which is grey, greasy, of uniform colour, soft, and glossy is the best.